DESCRIPTION: (provided by the applicant): In subSaharan Africa, the risk of malaria is due to exposure to infectious bites of mosquitoes, particularly Anopheles gambiae. There is a high degree of heterogeneity in the number of infectious bites that peoplewho live in endemic areas receive, which has implications for quantifying and ultimately reducing intensity of transmission. We hypothesize that this heterogeneity is due to aggregated production of adult mosquitoes from larval habitats, which is a function of oviposition site selection and larval habitat production. We believe that both of these processes are mediated by microorganisms that occur in larval habitats. Female mosquitoes will choose oviposition sites that emit volatile organic compounds(VOCs), which are generated by microbial metabolism of proteins (to indole and its derivatives) and humic acids (to phenolics). Secondly, we will quantify microbial processing of nutrients and accrual of microbial biomass in larval habitats, and link them to adult production. We believe that density-dependentlarval competition for nutrient-limited microbial food resources will limit adult production and will result in emergent females of variable, suboptimal body masses and nutrient reserves. These factors will in turn affect population regulatory processes and vectorial capacity attributes in An. Gambiae populations. Methods will involve spatial quantification of productive larval habitats in the Asembo Bay study site in western Kenya, a thoroughly mapped and well studied malaria endemic area. Microbial-mediation of oviposition site selection will be studied through characterization of the microbial community and emitted VOCs using GC/MS. GC/MS-electroantennogram detection of VOCs, and experimental oviposition site selection where microbes and VOCs are manipulated. Microbial basis for larval habitat production will be studied with field and lab experiments where nutrient sources and microbial communities are quantified, manipulated and larval growth responses and adult production quantified.